Paper takes on a semi-permanent set or curl by being bent, especially under heat. Other factors, such as printing on one side of paper, may also cause curl. Electrophotographic imaging typically involves bonding toner to paper using heat as a final step in imaging, which results in significant curling. Where the paper is to be conveyed further, such as for duplex printing on the opposite side to the first printing, decurling typically is employed to assure that the paper will feed reliably during the second printing operation.
U.S. Pat. No. 5,066,984 to Coombs teaches a decurler of the general kind in which this invention is employed. That patent employs a stationary guide in the form of in an arc spaced from and partially surrounding a rotating roller. The paper is fed between the guide and the roller, where it is bent around roughly 120 degrees of the roller. The roller is rotated in a direction which assists in paper feeding, but the contact with the roller is light because the space between the guide and the roller is more than the thickness of the paper.
Japanese patent 60-97162 to T. Hashimoto, issued May 30, 1985, discloses a flat guide spaced from pinch rollers for decurling.
The decurler of the foregoing patent 5,066,984 does not provide satisfactory results for papers of different rigidity. Configurations of the arc guide and the spaced roller may be satisfactory for one paper but produce under decurling or over decurling (curling in the direction opposite from the original curling) for other papers. This invention employs self-adjustment of the guide to achieve consistent and highly satisfactory results for papers within a wide range of rigidity.
U.S. Pat. No. 2,531,619 to Gonia discloses a decurler in which decurling is by directing paper around a spring-mounted roller for which the pressure is mechanically adjusted to vary the degree of flexing. This adjustment is done by adjusting screws and is not automatic.